The Samsung NU series has a high rate of backlight failures causing dark vertical bands or dark sections of the screen. See post here. The one repaired here has the right side dark. The backlights are edge lit from the bottom and running in Dynamic mode and at maximum level will tend to burn these out pretty quickly.
This model has two strips with each wired in left and right banks. Though only one side was bad, I replaced both with new strips. Part number is AOT_55_NU7300_NU7100_2X40_3030C There are a few sellers on ebay.
I was lucky and the light spreading inner panel was not burnt by the hot LEDs.
Edge lits are very finicky and any imperfection will cause an uneven backlight or bright spots.